Wide band noise generator



Oct. 17, 1967 F. 'r. GRIFFIN 3 9 WIDE BAND NOISE GENERATOR Filed June 26, 1959 INVENTOR FRED T. GRIFFIN BY Mw ATTORNEY United States Patent Navy Filed June 26, 1959, Ser. No. 823,268 3 Claims. (Cl. 331-78) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to a signal generator and in particular to a noise generator.

Noise generators in the prior art have at least two disadvantages: they lack adequate output power and uniform spectral distribution over a wide frequency range. In one type employing a photomultiplier tube only a few millivolts noise output is available, necessitating a wide-band video amplifier of 40 to 60 db gain to provide one volt of usable noise. In another type using a gas triode with a traverse magnetic field, such as the 6D4, a peak in the output occurs between 0.7 and 1 me. with the amplitude on the high frequency side down 30 to 45 db at 5 mc. Because of the nonuniformity within the 6D4 family, the design of a filter required to provide a flat output is extremely diflicult and must be a compromise that is unsatisfactory for a noise generator having a fiat output of only 5 mc.

Accordingly, it is an object of the present invention to provide a noise generator having a uniform spectral distribution and flat video output of comparatively large amplitude over a wide frequency range.

Other objects and advantages of the invention will become more fully apparent from the following description of the annexed drawings in which like reference numerals designate like parts throughout the figures and where- 1n:

FIG. 1 represents a counter tube employed in FIG. 2. FIG. 2 is a preferred embodiment of the present invention.

FIG. 3 represents a plot of frequency v. decibels of the signal provided by the embodiment shown in FIG. 2.

Briefly, a counter tube is operated so that only one target of a plurality provides an output while the others function as dummies. The .output of the target is 1 applied througha cathode follower and a frequency compensation circuit to obtain a signal with a comparatively large amplitude and uniform spectral distribution extending over a wide band of frequencies. I

Referring to FIG. 1, counter tube 10 consists of an indirectly heated cathode 11 surrounded by thirty elements geometrically arranged in ten groups. Each group is composed of a target 12, a switching grid 13, and a spade 14, thespade and switching grid being interposed between the target and cathode. Conventional magnetic field producing means, not shown, provide a magnetic field, indicated at 80 in FIG. 1, which is perpendicular to the electron flow between cathode 11 and the other tube elements. Under static conditions counter tube 10 is at current cut-off, but if any spade is lowered below a critical value, the altered field conditions cause the target to become conductive; if the potential on a switching grid adjacent to a conducting target is lowered, other conditions remaining equal, the electron beam shifts to the target associated with the switching grid.

Referring to FIG. 2, tar-get 15 is connected through resistor 16 to source of positive potential 17 and the remaining targets of counter tube 10 are connected together and through resistor 18 to the source of positive potential. Thus, all targets, except target 15, are maintained at 3,348,166 Patented Oct. 17, 1967 the same potential, the potential on target 15 being somewhat lower than that on the remaining targets due to the voltage drop across resistor 16 when the target draws current. Similarly, positive potential is applied from the center tap of variable resistor 22 through resistors 20 and 21 to spade 19 and through resistor 24 to the remaining spades of counter tube 10 so that all the spades, except spade 19, are maintained at the same potential. And, since resistors 25 and 26 form a voltage divider connected across source of positive potential 17, all the switching grids of counter tube 10 are maintained at the same potential through resistor 27.

Because spade 19 is connected through resistors 20 and 21 to the center tap of variable resistor 22, the current through target 15 may be controlled by varying the setting of variable resistor 22. In this way, under selected operat ing conditions, the target may draw the maximum permissible current.

Resistors 23 and 39 and variable resistor 22 form a voltage divider connected in parallel with source of positive potential 17 and ground, and resistors 33, 37 and terminal 38 likewise constitute a voltage divider in parallel with negative voltage 31 and ground. Finally, terminal 30, located between resistors 20 and 21, is connected. to source of negative potential 31 through gas discharge tube 32, terminal 38 and resistor 33, also to source of positive potential 17 through gas discharge tube 34 and resistor 35, and to ground through switch 36.

In operation, as indicated below, the difference in potential between terminal 30 and source of positive potential 17 ionizes gas discharge tube 34, Current through the gas discharge tube is limited by resistor 35 and the potential on terminal 30 is not disturbed. When ionized, gas discharge tube 34 indicates that spade 19, at lower potential than the remaining spades of counter tube 10, is causing target '15 to draw current, thereby developing a noise signal across resistor 16. This arrangement for indicating the presence of noise in the output of counter tube 10 is more infallible than measuring the current drawn by target 15, since a combination of conditions could occur, even though unstable, where target current could exist but where a noise signal would not appear.

Becausecounter tube 10 is of the magnetron type, too great an inductive load will cause coherent noise or ringing, resulting in a preponderance of one frequency or group of closely spaced frequencies in the output. To provide a uniform frequency distribution, target 15 is connected through capacitor 40 to the control grid of electron tube 41 in a cathode follower circuit having an in put capacitance of l or 2 ,uuf. The control grid of electron tube 41 is tied to the cathode through resistors 42 and 43 and to ground through resistors 42 and 44. One terminal of frequency compensation circuit 52, consisting of choke 53 in parallel with resistor 54, is connected to the cathode of electron tube 41 and the other is coupled to the control grid of electron tube 56 through capacitor 55. The cathode of electron tube 56 is grounded through resistor 57, the screen grid is grounded through capacitor 61 and also through resistor 62. The control grid of the latter electron tube is connected to the cathode through resistors 57 and 59, and finally, positive potential source 17 is applied to the plate through resistor 64 and choke -63 and flat at higher frequencies. Similarly, for the same purpose, choke 63 and resistor 64 form a compensation network with the capacitances of electron tube 56. It is understood that other types of conventional compensation circuits could be used instead of those indicated immediately above.

Completing the description of FIG. 2, potential is applied directly from source of positive potential 17 to the plate of electron tube 71, the control grid of the electron tube is tied to the cathode through resistors 72 and 74, andv the cathode is coupled to output terminal 75 through capacitor 76 and is grounded through resistors 72 and 73.

The following table sets forth electron tubes and values of potential, inductances, and impedances which have been found satisfactory in the operation of the embodiment in FIG. 2. It should be understood that the table is exemplary only and is not to be interpreted in a limiting sense.

Source of positive potential 17 (regulated) volts 150 Source of negative potential 31 do 150 Potential at the center tap of variable resistor 22, approx. a volts 75 Potential at terminal 38 approx. do -2() Counter tube 6700 Gas discharge tubes 32 and 34 Neon tubes, NE-l Electron tubes 41 and 71 6BQ7/2 Electron tube 56 5842 Resistors 16 and 18 (1 W.) 1.8K Resistors 20, 21, 24, and 27 100K Variable resistor 22 50K Resistors 23, 26, and 62 56K Resistors 25 and 37 27K Resistor 33 180K Resistor 35 500K Resistor 44 1K Resistors 54 and 69 3K Resistor 57 ohms 120 Resistor 59 150K Resistor 60 6.8K Resistor 64 (2 W.) 1.5K Resistor 73 2K Capacitors-40, 55, 70', and 76 .z.f. 0.02 Capacitor 61 0.1 Choke 53 h." 7 Resistor 39 22K Resistors 42 and 74 750K Resistors 43 and 72 ohms 270 Choke 63 ,uh 2 Choke uh 9 NOTE.All resistors /2 watt except where noted.

In the operation of the embodiment in FIG. 2, since the potential at terminal 38 is ---20 volts and that at the center tap of variable resistor 22 is 75 volts, the volttage across gas discharge tube 32 exceeds the firing potential and the gas discharge tube conducts elfectively grounding spade 19 through terminal 30. Spade '19, being at a lower potential than the remaining spades of counter tube 10, target conducts bringing its associated spade 19 to cathode potential, e.g., approximately ground. Resistors and 21 then function as a voltage divider across the 75 volts on the center tap of variable resistor 22, providing approximately 37%. volts on terminal so that the potential across gas discharge tube 32 will be less than ionization potential and the gas discharge tube will no longer conduct.

Since the potential on terminal 30 is approximately 37 /2 volts and that of source of positive potential 17 is volts, gas discharge tube 34 conducts indicating that spade 19 is at a lower potential than the remaining spades and that a noise signal is being developed across load resistor 16 and applied to the. grid of electron tube 41.

The noise signal, appearing across resistors 43 and 44, is

applied to electron tube 56 and,after amplification and frequency compensation, is coupled to the control grid of electron tube 71, thereby developing the signal represented in FIG. 3 at output terminal 75. For the typical values and components set forth above, this signal has an amplitude of 1 volt RMS and is flat from 50 kc. to 10 me. with a plus or minus 2.8 db variation.

The wide band frequency characteristic of the device of this invention, as shown in FIG. 3, is in sharp contrast to the narrow band characteristic of a simple magnetron noise source. The notably superior output which is obtained using a beam switching type of magnetron, as described, is presently considered a phenomenon. According to one theory, not fully advanced, this superior output may be attributed to interaction amongst the plurality of crossed electric and magnetic fields within the device of this invention.

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined by the appended claims, as only a preferred embodiment thereof has been disclosed.

What is claimed is:

1. A noise generator comprising a magnetron having a cathode and a plurality of individual anode systems substantially uniformly disposed in coplanar relation with respect to each other and disposed about said cathode in concentric relation thereto, each of said anode systems including a beam target and, at least one beam forming means interposed said cathode and its respective target,

and magnetic field means disposed to produce a magnetic field in transverse relation with respect to the plane of said anode systems; means connected to said beam forming means in at least one of said anode systems for producing at least one electron beam between said cathode and said anode systems; and means connected to said beam forming means in the remainder of said anode systems maintaining each respective anode system at a positive potential with respect to said cathode, the magnitude of the potential difference between said cathode and said remainder of said anodesystems being in the vicinity of and less than that magnitude required to produce an electron beam therebetween.

2. The noise generator as defined in claim 1 wherein each of said beam forming means of said anode systems includes a spade element.

3. The noise generator as defined in claim 2 wherein said beam forming means in the remainder of said anode systems are electrically connected in common.

References Cited UNITED STATES PATENTS 2,658,149 11/1953 Gallagher et al. 331-78 2,746,277 5/ 1956 Haagensen 33178 ROY LAKE, Primary Examiner.

C. L. JUSTUS, Examiner.

T. D. JENNINGS, Assistant Examiner. 

1. A NOISE GENERATOR COMPRISING A MAGNETRON HAVING A CATHODE AND A PLURALITY OF INDIVIDUAL ANODE SYSTEMS SUBSTANTIALLY UNIFORMLY DISPOSED IN COPLANAR RELATION WITH RESPECT TO EACH OTHER AND DISPOSED ABOUT SAID CATHODE IN CONCENTRIC RELATION THERETO, EACH OF SAID ANODE SYSTEMS INCLUDING A BEAM TARGET AND, AT LEAST ONE BEAM FORMING MEANS INTERPOSED SAID CATHODE AND ITS RESPECTIVE TARGET, AND MAGNETIC FIELD MEANS DISPOSED TO PRODUCE A MAGNETIC FIELD IN TRANSVERSE RELATION WITH RESPECT TO THE PLANE OF SAID ANODE SYSTEMS; MEANS CONNECTED TO SAID BEAM FORMING MEANS IN AT LEAST ONE OF SAID ANODE SYSTEMS FOR PRODUCING AT LEAST ONE ELECTRON BEAM BETWEEN SAID CATHODE 